In a conventional vehicle auxiliary power supply, a configuration is typically such that a blocking diode is inserted between a pantograph and a filter capacitor that smooths a voltage applied from an overhead line via the pantograph, and a snubber circuit is provided in parallel with the blocking diode (see, for example, Non Patent Literature 1 described below).
Because many electrical devices having relatively large rated power are mounted on the railway vehicle, a large current flows to the blocking diode. Furthermore, during an operation of the railway vehicle, a current flows constantly to the blocking diode. Therefore, a cooler (for example, a cooling fin) is generally provided in the blocking diode so that the temperature of the blocking diode does not exceed a tolerance. The snubber circuit connected in parallel with the blocking diode inevitably becomes large due to the large capacity of the blocking diode.